A combined hammer and levelling device is known in the prior art for example U.S. Pat. No. 1,702,689 and U.S. Pat. No. 3,119,424.
In the former patent a level vial is incorporated in the shaft of a hammer. To enable the hammer to be used as a level, the shaft is held parallel to the workpiece to be level tested by mean of two support points, one being the flat surface of the striking face of the hammer and the other the end of an adjustable support arm attached to the end of the shaft. Consequently the axis of the level vial in the shaft may be arranged such that it is either normal or parallel to a plane containing the end of the support arm when extended and the flat striking face of the hammer, i.e. the plane of the workpiece.
The disadvantage of this design lies in the incorporation of the support arm on the end of the shaft which has to be swung between two positions as between when the device is being used as a hammer and when as a level. This imposes a necessary interference factor on the operator, and time is wasted in switching from one function to another.